PDF(Pubmed)
Abstract：
Volume-regulated anion channels (VRACs) are hexamers of LRRC8 proteins that are crucial for cell volume regulation. N termini (NTs) of the obligatory LRRC8A subunit modulate VRACs activation and ion selectivity, but the underlying mechanisms remain poorly understood. Here, we report a 2.8-Å cryo-electron microscopy structure of human LRRC8A that displays well-resolved NTs. Amino-terminal halves of NTs fold back into the pore and constrict the permeation path, thereby determining ion selectivity together with an extracellular selectivity filter with which it works in series. They also interact with pore-surrounding helices and support their compact arrangement. The C-terminal halves of NTs interact with intracellular loops that are crucial for channel activation. Molecular dynamics simulations indicate that low ionic strength increases NT mobility and expands the radial distance between pore-surrounding helices. Our work suggests an unusual pore architecture with two selectivity filters in series and a mechanism for VRAC activation by cell swelling.
摘要：
体积调节阴离子通道（VRAC）是LRRC8蛋白的六聚体，对细胞体积调节至关重要。强制性LRRC8A亚基的N末端（NT）调节VRACs活化和离子选择性，但潜在的机制仍然知之甚少。这里,我们报告了人类LRRC8A的2.8-µ低温电子显微镜结构，显示出分辨率良好的NT。NTs的氨基末端一半折回孔中并收缩渗透路径，从而确定离子选择性以及与其串联工作的细胞外选择性过滤器。它们还与孔周围的螺旋相互作用并支持它们的紧凑排列。NT的C末端一半与细胞内环相互作用，这对于通道激活至关重要。分子动力学模拟表明，低离子强度增加了NT的迁移率，并扩大了孔周围螺旋之间的径向距离。我们的工作表明了一种不寻常的孔结构，具有两个串联的选择性过滤器以及通过细胞膨胀激活VRAC的机制。
